Amazon Redshift deep dive on storage and query processing

Deep Dive on Amazon Redshift
Storage Subsystem and Query Life Cycle
Tony Gibbs, Data Warehousing Solutions Architect
June 2017

Deep Dive Overview
• Amazon Redshift History and Development
• Cluster Architecture
• Concepts and Terminology
• Storage Deep Dive
• Design Considerations
• Query Life Cycle
• Loading Best Practices
• New & Upcoming Feature
• Open Q&A

Amazon Redshift History & Development

Columnar
MPP
OLAP
AWS IAMAmazon VPCAmazon SWF
Amazon S3 AWSKMS Amazon
Route 53
Amazon
CloudWatch
Amazon EC2
PostgreSQL Amazon Redshift

February 2013
June 2017
> 100 Significant Patches
> 150 Significant Features

Amazon Redshift Cluster Architecture

Redshift Cluster Architecture
• Massively parallel, shared nothing
• Leader node
– SQL endpoint
– Stores metadata
– Coordinates parallel SQL processing
• Compute nodes
– Local, columnar storage
– Executes queries in parallel
– Load, backup, restore
10 GigE
(HPC)
Ingestion
Backup
Restore
SQL Clients/BI Tools
128GB RAM
16TB disk
16 cores
S3 / EMR / DynamoDB / SSH
JDBC/ODBC
128GB RAM
16TB disk
16 coresCompute
Node
128GB RAM
16TB disk
16 coresCompute
Node
128GB RAM
16TB disk
16 coresCompute
Node
Leader
Node

128GB RAM
16TB disk
16 cores
128GB RAM
16TB disk
16 cores
Compute Node
128GB RAM
16TB disk
16 cores
Compute Node
128GB RAM
16TB disk
16 cores
Compute Node
Leader Node

128GB RAM
16TB disk
16 cores
128GB RAM
16TB disk
16 cores
Compute Node
128GB RAM
16TB disk
16 cores
Compute Node
128GB RAM
16TB disk
16 cores
Compute Node
Leader Node
• Parser & Rewriter
• Planner & Optimizer
• Code Generator
• Input: Optimized plan
• Output: >=1 C++ functions
• Compiler
• Task Scheduler
• WLM
• Admission
• Scheduling
• PostgreSQL Catalog Tables

128GB RAM
16TB disk
16 cores
128GB RAM
16TB disk
16 cores
Compute Node
128GB RAM
16TB disk
16 cores
Compute Node
128GB RAM
16TB disk
16 cores
Compute Node
Leader Node
• Query execution processes
• Backup & restore processes
• Replication processes
• Local Storage
• Disks
• Slices
• Tables
• Columns
• Blocks

Designed for I/O Reduction
• Columnar storage
• Data compression
• Zone maps
aid loc dt
1 SFO 2016-09-01
2 JFK 2016-09-14
3 SFO 2017-04-01
4 JFK 2017-05-14
• Accessing dt with row storage:
– Need to read everything
– Unnecessary I/O
aid loc dt
CREATE TABLE loft_deep_dive (
aid INT --audience_id
,loc CHAR(3) --location
,dt DATE --date
);

• Zone maps
aid loc dt
1 SFO 2016-09-01
2 JFK 2016-09-14
3 SFO 2017-04-01
4 JFK 2017-05-14
• Accessing dt with columnar storage:
– Only scan blocks for relevant
column
aid loc dt
,dt DATE --date
);

• Zone maps
aid loc dt
1 SFO 2016-09-01
2 JFK 2016-09-14
3 SFO 2017-04-01
4 JFK 2017-05-14
• Columns grow and shrink independently
• Effective compression ratios due to like data
• Reduces storage requirements
• Reduces I/O
aid loc dt
aid INT ENCODE LZO
,loc CHAR(3) ENCODE BYTEDICT
,dt DATE ENCODE RUNLENGTH
);

• Zone maps
aid loc dt
1 SFO 2016-09-01
2 JFK 2016-09-14
3 SFO 2017-04-01
4 JFK 2017-05-14
aid loc dt
,dt DATE --date
);
• In-memory block metadata
• Contains per-block MIN and MAX value
• Effectively prunes blocks which cannot
contain data for a given query
• Eliminates unnecessary I/O

SELECT COUNT(*) FROM LOGS WHERE DATE = '09-JUNE-2013'
MIN: 01-JUNE-2013
MAX: 20-JUNE-2013
MIN: 08-JUNE-2013
MAX: 30-JUNE-2013
MIN: 12-JUNE-2013
MAX: 20-JUNE-2013
MIN: 02-JUNE-2013
MAX: 25-JUNE-2013
Unsorted Table
MIN: 01-JUNE-2013
MAX: 06-JUNE-2013
MIN: 07-JUNE-2013
MAX: 12-JUNE-2013
MIN: 13-JUNE-2013
MAX: 18-JUNE-2013
MIN: 19-JUNE-2013
MAX: 24-JUNE-2013
Sorted By Date
Zone Maps

Terminology and Concepts: Data Sorting
• Goals:
• Physically order rows of table data based on certain column(s)
• Optimize effectiveness of zone maps
• Enable MERGE JOIN operations
• Impact:
• Enables rrscans to prune blocks by leveraging zone maps
• Overall reduction in block I/O
• Achieved with the table property SORTKEY defined over one or more columns
• Optimal SORTKEY is dependent on:
• Query patterns
• Data profile
• Business requirements

Terminology and Concepts: Slices
• A slice can be thought of like a “virtual compute node”
– Unit of data partitioning
– Parallel query processing
• Facts about slices:
– Each compute node has either 2, 16, or 32 slices
– Table rows are distributed to slices
– A slice processes only its own data

Data Distribution
• Distribution style is a table property which dictates how that table’s data is
distributed throughout the cluster:
• KEY: Value is hashed, same value goes to same location (slice)
• ALL: Full table data goes to first slice of every node
• EVEN: Round robin
• Goals:
• Distribute data evenly for parallel processing
• Minimize data movement during query processing
KEY
ALL
Node 1
Slice 1 Slice 2
Node 2
Slice 3 Slice 4
Node 1
Slice 1 Slice 2
Node 2
Slice 3 Slice 4
Node 1
Slice 1 Slice 2
Node 2
Slice 3 Slice 4
EVEN

Data Distribution: Example
,dt DATE --date
) DISTSTYLE (EVEN|KEY|ALL);
CN1
Slice 0 Slice 1
CN2
Slice 2 Slice 3
Table: loft_deep_dive
User Columns System Columns
aid loc dt ins del row

Data Distribution: EVEN Example
,dt DATE --date
) DISTSTYLE EVEN;
CN1
Slice 0 Slice 1
CN2
Slice 2 Slice 3
INSERT INTO loft_deep_dive VALUES
(1, 'SFO', '2016-09-01'),
(2, 'JFK', '2016-09-14'),
(3, 'SFO', '2017-04-01'),
(4, 'JFK', '2017-05-14');
Rows: 0 Rows: 0 Rows: 0 Rows: 0
(3 User Columns + 3 System Columns) x (4 slices) = 24 Blocks (24MB)

Data Distribution: KEY Example #1
,dt DATE --date
) DISTSTYLE KEY DISTKEY (loc);
CN1
Slice 0 Slice 1
CN2
Slice 2 Slice 3
(1, 'SFO', '2016-09-01'),
(2, 'JFK', '2016-09-14'),
(3, 'SFO', '2017-04-01'),
(4, 'JFK', '2017-05-14');
Rows: 2 Rows: 0 Rows: 0
Rows: 0Rows: 1
Rows: 2Rows: 0Rows: 1

Data Distribution: KEY Example #2
,dt DATE --date
) DISTSTYLE KEY DISTKEY (aid);
CN1
Slice 0 Slice 1
CN2
Slice 2 Slice 3
(1, 'SFO', '2016-09-01'),
(2, 'JFK', '2016-09-14'),
(3, 'SFO', '2017-04-01'),
(4, 'JFK', '2017-05-14');

Data Distribution: ALL Example
,dt DATE --date
) DISTSTYLE ALL;
CN1
Slice 0 Slice 1
CN2
Slice 2 Slice 3
(1, 'SFO', '2016-09-01'),
(2, 'JFK', '2016-09-14'),
(3, 'SFO', '2017-04-01'),
(4, 'JFK', '2017-05-14');
Rows: 0 Rows: 0
(3 User Columns + 3 System Columns) x (2 slice) = 12 Blocks (12MB)
Rows: 0Rows: 1Rows: 2Rows: 4Rows: 3
Rows: 0Rows: 1Rows: 2Rows: 4Rows: 3

Terminology and Concepts: Data Distribution
• KEY
– The key creates an even distribution of data
– Joins are performed between large fact/dimension tables
– Optimizing merge joins and group by
• ALL
– Small and medium size dimension tables (< 2-3M)
• EVEN
– When key cannot produce an even distribution

Storage Deep Dive: Disks
• Redshift utilizes locally attached storage devices
• Compute nodes have 2.5-3x the advertised storage capacity
• 1, 3, 8, or 24 disks depending on node type
• Each disk is split into two partitions
– Local data storage, accessed by local CN
– Mirrored data, accessed by remote CN
• Partitions are raw devices
– Local storage devices are ephemeral in nature
– Tolerant to multiple disk failures on a single node

Storage Deep Dive: Blocks
• Column data is persisted to 1MB immutable blocks
• Each block contains in-memory metadata:
– Zone Maps (MIN/MAX value)
– Location of previous/next block
• Blocks are individually compressed with 1 of 10 encodings
• A full block contains between 16 and 8.4 million values

Storage Deep Dive: Columns
• Column: Logical structure accessible via SQL
• Physical structure is a doubly linked list of blocks
• These blockchains exist on each slice for each column
• All sorted & unsorted blockchains compose a column
• Column properties include:
– Distribution Key
– Sort Key
– Compression Encoding
• Columns shrink and grow independently, 1 block at a time
• Three system columns per table-per slice for MVCC

Block Properties: Design Considerations
• Small writes:
• Batch processing system, optimized for processing massive amounts of data
• 1MB size + immutable blocks means that we clone blocks on write so as not to
introduce fragmentation
• Small write (~1-10 rows) has similar cost to a larger write (~100 K rows)
• UPDATE and DELETE:
• Immutable blocks means that we only logically delete rows on UPDATE or DELETE
• Must VACUUM or DEEP COPY to remove ghost rows from table

Column Properties: Design Considerations
• Compression:
• COPY automatically analyzes and compresses data when loading into empty tables
• ANALYZE COMPRESSION checks existing tables and proposes optimal
compression algorithms for each column
• Changing column encoding requires a table rebuild
• DISTKEY and SORTKEY significantly influence performance (orders of magnitude)
• Distribution Keys:
• A poor DISTKEY can introduce data skew and an unbalanced workload
• A query completes only as fast as the slowest slice completes
• Sort Keys:
• A sortkey is only effective as the data profile allows it to be
• Selectivity needs to be considered

Storage Deep Dive: Slices
• Each compute node has either 2, 16, or 32 slices
• A slice can be thought of like a “virtual compute node”
– Unit of data partitioning
– Parallel query processing
• Facts about slices:
– Table rows are distributed to slices
– A slice processes only its own data
– Within a compute node all slices read from and write to all disks

128GB RAM
16TB disk
16 cores
128GB RAM
16TB disk
16 cores
Compute Node
128GB RAM
16TB disk
16 cores
Compute Node
128GB RAM
16TB disk
16 cores
Compute Node
Leader Node
• Parser & Rewriter
• Planner & Optimizer
• Code Generator
• Input: Optimized plan
• Output: >=1 C++ functions
• Compiler
• Task Scheduler
• WLM
• Admission
• Scheduling
• PostgreSQL Catalog Tables
• Redshift System Tables (STV)

Query Execution Terminology
• Step: An individual operation needed during query execution. Steps need to be
combined to allow compute nodes to perform a join. Examples: scan, sort,
hash, aggr
• Segment: A combination of several steps that can be done by a single process.
The smallest compilation unit executable by a slice. Segments within a stream
run in parallel.
• Stream: A collection of combined segments which output to the next stream or
SQL client.

Visualizing Streams, Segments, and Steps
Stream 0
Segment 0
Step 0 Step 1 Step 2
Segment 1
Step 0 Step 1 Step 2 Step 3 Step 4
Segment 2
Step 0 Step 1 Step 2 Step 3
Segment 3
Step 0 Step 1 Step 2 Step 3 Step 4 Step 5
Stream 1
Segment 4
Segment 5
Segment 6
Stream 2
Segment 7
Step 0 Step 1
Segment 8
Step 0 Step 1
Time

client
JDBC ODBC
Leader Node
Parser
Query Planner
Code Generator
Final Computations
Generate code for
all segments of
one stream
Explain Plans
Compute Node
Receive Compiled Code
Run the Compiled Code
Return results to Leader
Compute Node
Receive Compiled Code
Run the Compiled Code
Return results to Leader
Return results to client
Segments in a stream are
executed concurrently.
Each step in a segment is
executed serially.
Query Lifecycle

Query Execution Deep Dive: Leader Node
1. The leader node receives the query and parses the SQL.
2. The parser produces a logical representation of the original query.
3. This query tree is input into the query optimizer (volt).
4. Volt rewrites the query to maximize its efficiency. Sometimes a single query will be
rewritten as several dependent statements in the background.
5. The rewritten query is sent to the planner which generates >= 1 query plans for the
execution with the best estimated performance.
6. The query plan is sent to the execution engine, where it’s translated into steps,
segments, and streams.
7. This translated plan is sent to the code generator, which generates a C++ function
for each segment.
8. This generated C++ is compiled with gcc to a .o file and distributed to the compute
nodes.

Query Execution Deep Dive: Compute Nodes
• Slices execute the query segments in parallel.
• Executable segments are created for one stream at a time. When the segments
of that stream are complete, the engine generates the segments for the next
stream.
• When the compute nodes are done, they return the query results to the leader
node for final processing.
• The leader node merges the data into a single result set and addresses any
needed sorting or aggregation.
• The leader node then returns the results to the client.

Query Execution
Stream 0
Segment 0
Segment 1
Segment 2
Segment 3
Stream 1
Segment 4
Segment 5
Segment 6
Stream 2
Segment 7
Step 0 Step 1
Segment 8
Step 0 Step 1
Time
Stream 0
Segment 0
Segment 1
Segment 2
Segment 3
Stream 1
Segment 4
Segment 5
Segment 6
Stream 2
Segment 7
Step 0 Step 1
Segment 8
Step 0 Step 1
Stream 0
Segment 0
Segment 1
Segment 2
Segment 3
Stream 1
Segment 4
Segment 5
Segment 6
Stream 2
Segment 7
Step 0 Step 1
Segment 8
Step 0 Step 1
Stream 0
Segment 0
Segment 1
Segment 2
Segment 3
Stream 1
Segment 4
Segment 5
Segment 6
Stream 2
Segment 7
Step 0 Step 1
Segment 8
Step 0 Step 1
Slices
0
1
2
3

Parallelism considerations with Redshift slices
DS2.8XL Compute Node
• Ingestion Throughput:
– Each slice’s query processors can load one file at a time:
• Streaming decompression
• Parse
• Distribute
• Write
• Realizing only partial node usage as 6.25% of slices are active
0 2 4 6 8 10 12 141 3 5 7 9 11 13 15

Design considerations for Redshift slices
• Use at least as many input
files as there are slices in the
cluster
• With 16 input files, all slices
are working so you maximize
throughput
• COPY continues to scale
linearly as you add nodes
16 Input Files
DS2.8XL Compute Node
0 2 4 6 8 10 12 141 3 5 7 9 11 13 15

Data Preparation
• Export Data from Source System
– CSV Recommend (Simple Delimiter '|' or ’,')
• Be aware of UTF-8 varchar columns (UTF-8 take 4 bytes per char)
• Be aware of your NULL character (N)
– GZIP Compress Files
– Split Files (1MB – 1GB after gzip compression)
• Useful COPY Options for PoC Data
– MAXERRORS
– ACCEPTINVCHARS
– NULL AS

Fast @ exabyte scale Elastic & highly available On-demand, pay-per-query
High concurrency:
Multiple clusters access
same data
No ETL: Query data in-
place using open file
formats
Full Amazon Redshift
SQL support
S3
SQL
Run SQL queries directly against data in S3 using thousands of nodes
Recently Released Features: Amazon Redshift Spectrum

• Amazon Redshift Spectrum seamlessly integrates with your existing SQL & BI
apps
• Support for complex joins, nested queries & window functions
• Support for data partitioned in S3 by any key
Date, time, and any other custom keys
e.g., year, month, day, hour
Recently Released Features: Amazon Redshift Spectrum

Query
SELECT COUNT(*)
FROM S3.EXT_TABLE
GROUP BY…
Amazon
Redshift
JDBC/ODBC
...
1 2 3 4 N
Amazon S3
Exabyte-scale object storage
Data Catalog
Apache Hive Metastore

Recently Released Features
QMR - Query Monitoring Rules
• Apply rules to inflight queries
New Data Type - TIMESTAMPTZ
• Support for Timestamp with Time zone : New TIMESTAMPTZ data type to input complete timestamp values that
include the date, the time of day, and a time zone.
Eg: 30 Nov 07:37:16 2016 PST
Multi-byte Object Names
• Support for Multi-byte (UTF-8) characters for tables, columns, and other database object names
User Connection Limits
• You can now set a limit on the number of database connections a user is permitted to have open concurrently
Automatic Data Compression for CTAS
• All newly created tables will leverage default encoding
New Column Encoding ZSTD

Recently Released Features
Performance Enhancements
• Vacuum (10x faster for deletes)
• Snapshot Restore (2x faster)
• Queries (Up to 5x faster)
Copy Can Extend Sorted Region on Single Sort Key
• No need to vacuum when loading in sorted order
Enhanced VPC Routing
• Restrict S3 Bucket Access
Schema Conversion Tool - One-Time Data Exports
• Oracle, Teradata, SQL Server
Schema Conversion Tool
• Vertica, SQL Server, Netezza and Greenplum

BI tools SQL clientsAnalytics tools
Client AWS
Redshift
ADFS
Corporate
Active Directory IAM
Amazon Redshift
ODBC/JDBC
User groups Individual user
Single Sign-On
Identity providers
New Redshift
ODBC/JDBC
drivers. Grab the
ticket (userid) and
get a SAML
assertion.
Coming Soon: IAM Authentication

Coming Soon: Lots More …
Automatic and Incremental Background VACUUM
• Reclaims space and sorts when Amazon Redshift clusters are idle
• Vacuum is initiated when performance can be enhanced
• Improves ETL and query performance
Short Query Bias
• Prioritize interactive short running queries
010101010101

Resources
• https://github.com/awslabs/amazon-redshift-utils
• https://github.com/awslabs/amazon-redshift-monitoring
• https://github.com/awslabs/amazon-redshift-udfs
• Admin scripts
Collection of utilities for running diagnostics on your cluster
• Admin views
Collection of utilities for managing your cluster, generating schema DDL, etc.
• ColumnEncodingUtility
Gives you the ability to apply optimal column encoding to an established schema with
data already loaded
• Amazon Redshift Engineering’s Advanced Table Design Playbook
https://aws.amazon.com/blogs/big-data/amazon-redshift-engineerings-advanced-table-design-playbook-preamble-prerequisites-and-
prioritization/

Tony Gibbs
aws.amazon.com/activate
Thank you!

Amazon Redshift deep dive on storage and query processing

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